Struct wasm_bindgen::JsError

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pub struct JsError { /* private fields */ }
Expand description

Convenience type for use on exported fn() -> Result<T, JsError> functions, where you wish to throw a JavaScript Error object.

You can get wasm_bindgen to throw basic errors by simply returning Err(JsError::new("message")) from such a function.

For more complex error handling, JsError implements From<T> where T: std::error::Error by converting it to a string, so you can use it with ?. Many Rust error types already do this, and you can use thiserror to derive Display implementations easily or use any number of boxed error types that implement it already.

To allow JavaScript code to catch only your errors, you may wish to add a subclass of Error in a JS module, and then implement Into<JsValue> directly on a type and instantiate that subclass. In that case, you would not need JsError at all.

Basic example

use wasm_bindgen::prelude::*;

#[wasm_bindgen]
pub fn throwing_function() -> Result<(), JsError> {
    Err(JsError::new("message"))
}

Complex Example

use wasm_bindgen::prelude::*;

#[derive(Debug, Clone)]
enum MyErrorType {
    SomeError,
}

use core::fmt;
impl std::error::Error for MyErrorType {}
impl fmt::Display for MyErrorType {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "display implementation becomes the error message")
    }
}

fn internal_api() -> Result<(), MyErrorType> {
    Err(MyErrorType::SomeError)
}

#[wasm_bindgen]
pub fn throwing_function() -> Result<(), JsError> {
    internal_api()?;
    Ok(())
}

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impl JsError

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pub fn new(s: &str) -> JsError

Construct a JavaScript Error object with a string message

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impl Clone for JsError

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fn clone(&self) -> JsError

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl<E> From<E> for JsErrorwhere E: Error,

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fn from(error: E) -> Self

Converts to this type from the input type.
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impl From<JsError> for JsValue

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fn from(error: JsError) -> Self

Converts to this type from the input type.
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impl IntoWasmAbi for JsError

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type Abi = <JsValue as IntoWasmAbi>::Abi

The wasm ABI type that this converts into when crossing the ABI boundary.
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fn into_abi(self) -> Self::Abi

Convert self into Self::Abi so that it can be sent across the wasm ABI boundary.

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Blanket Implementations§

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impl<T> Any for Twhere T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for Twhere T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for Twhere T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<!> for T

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fn from(t: !) -> T

Converts to this type from the input type.
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for Twhere U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> ReturnWasmAbi for Twhere T: IntoWasmAbi,

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type Abi = <T as IntoWasmAbi>::Abi

Same as IntoWasmAbi::Abi
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fn return_abi(self) -> <T as ReturnWasmAbi>::Abi

Same as IntoWasmAbi::into_abi, except that it may throw and never return in the case of Err.
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impl<T> ToOwned for Twhere T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.